Renders LoginPage with form.rateLimited=true and asserts that the
role="alert" div (clock icon + error message) is visible in the browser.
Previously only the form action's rateLimited=true return value was tested;
now the rendered UI is also verified.
Addresses Sara Concern 4 / Elicit open question from PR #617 review.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>